A conventional semiconductor integrated circuit includes a plurality of functional devices formed on a chip, an input buffer circuit including a plurality of inverters connected between input terminals and the functional devices, and an output buffer circuit including a plurality of inverters connected between output terminals and the functional devices.
In testing the conventional semiconductor integrated circuit, a predetermined pattern of voltage signal consisting of V.sub.DD and ground levels is applied to input terminals as high and low signals, and a pattern of voltage signals is detected at output terminals. When the detected pattern is a predetermined output pattern, it is determined that the semiconductor integrated circuit has been fabricated to have a predetermined IC pattern including transistors, interconnections, etc. If not so, it is determined to be defective.
This IC pattern test is carried out separately for each one of functional devices provided in the semiconductor integrated circuit, because the functional devices are connected through input and output buffers to corresponding ones of the input and output terminals. In this IC pattern test, interconnections of the functional devices are also checked in the same manner as described above.
After it is determined to stand the test, a predetermined pattern of voltage signals consisting of, for instance, V .sub.DD .times.0.7(V.sub.IH) and V.sub.DD .times.0.3 (V.sub.IL) is applied to the input terminals as high and low signals. When a predetermined pattern of voltage signals is detected at the output terminals, an input characteristic of the input buffer is determined to meet the standard. Then, a predetermined pattern of voltage signals consisting of V.sub.DD and ground levels is applied to the input terminals to check a pattern of voltage signals at the output terminals. In this pattern detection at the output terminals, V.sub.DD .times.0.7 (V.sub.OH) and V.sub.DD .times.0.3 (V.sub.OL) are used as reference voltage for high and low levels, and output voltages are detected by measuring voltage up (increase) and decrease (drop) between a tester and each output terminal, to which the tester is connected to draw current therefrom and to supply current thereto dependent on levels of the output terminals. Thus, an output characteristic of the output buffer is examined. In addition, an input and output characteristic of the input and output buffers is examined by applying a predetermined pattern of voltage signals consisting of the V.sub.IH and V.sub.IL levels to the input terminals and detecting a pattern of voltage signal at the output terminals according to the reference voltages of the V.sub.OH and V.sub.OL levels.
As described above, the check of an IC pattern including transistors, interconnections, etc., and that of input, output, and input and output characteristics of the input and output buffers are carried out.
According to the conventional semiconductor integrated circuit, however, there is a disadvantage in that the test of the input and output buffers is complicated, because a considerable number of test patterns which are used for the test of the functional devices are utilized.
Additionally, there is a further disadvantage in that a program for the test of the input and output buffer is long and complicated, because the test continues during the conduct of a starting number of the test pattern to a predetermined number thereof, and the test such as the aforementioned V.sub.OH /V.sub.OL check is carried out under the predetermined number of the test pattern by using the tester, so that the number of test is extraordinarily large.